Author: Assoc Prof Patrick Emanuel, Dermatopathologist, Auckland, New Zealand, 2013.
Epithelioid cell histiocytoma is a well recognised variant of cutaneous fibrous histiocytoma that may be confused with other benign and malignant mesenchymal lesions. It is otherwise known as epithelioid fibrous histiocytoma and epithelioid dermatofibroma.
Histology of epithelioid histiocytoma
In epithelioid histiocytoma, sections show a centrally located, circumscribedtumour underlying an epidermal collarette (figure 1). The tumour is composed of epithelioid cells arranged in sheets and sometimes a storiform pattern. Individual cells show abundant eosinophilic cytoplasm with round vesicular nuclei and prominent nucleoli (figures 2-4). The cells may be markedly enlarged and display some nuclear atypia (figure 4).
There is frequently an associated inflammatory cell infiltrate which can be helpful for the diagnosis (figure 3). Some mitoses may be seen. Multinucleated giant cells and haemosiderindeposition are also sometimes seen.